1. Field of the Invention
The present invention relates generally to an apparatus for selectively varying the reflectance of electromagnetic energy from an object surface and, more particularly, such apparatus of mechanical electrical construction which operates over a relatively wide reflectance dynamic range, has low power requirements, and higher switching speed compared to other known reflectance control measures.
2. Description of Related Art
There are many situations in which the surface of an object or craft may experience a substantial exposure to radiation in the thermal band (3-18 microns), for example, requiring considerable dissipation in order to protect the object from deleterious results or even total destruction. It is particularly true of a space craft which may be exposed on one surface to a very high amount of thermal band radiation while adjacent surfaces remain potentially radiation free, the resulting high temperature differential of the space craft posing additional danger. Accordingly, it is desirable to have some way for selectively controlling reflectance from the surface of a craft or other object in order to manage the amount of heat induced into the object and, in that way, maintain the temperature within appropriate limits.
In the past, devices operating on a chemical and electrical basis, referred to generally as electrochromics, have been used for reflectance control. These devices have been found to experience chemical breakdown on exposure to ultraviolet radiation making them substantially inoperative for the desired reflectance variation purposes. Also, electrochromics devices are life cycle limited, have limited operational dynamic ranges and relatively slow switching cycle times, all of which leave them less than fully satisfactory for practical use.